Transcriptome Profiling and Functional Analysis ofAgrobacterium tumefaciensReveals a General Conserved Response to Acidic Conditions (pH 5.5) and a Complex Acid-Mediated Signaling Involved inAgrobacterium-Plant Interactions

Abstract

Agrobacterium tumefaciens transferred DNA (T-DNA) transfer requires that the virulence genes (vir regulon) on the tumor-inducing (Ti) plasmid be induced by plant phenolic signals in an acidic environment. Using transcriptome analysis, we found that these acidic conditions elicit two distinct responses: (i) a general and conserved response through which Agrobacterium modulates gene expression patterns to adapt to environmental acidification and (ii) a highly specialized acid-mediated signaling response involved in Agrobacterium-plant interactions. Overall, 78 genes were induced and 74 genes were repressed significantly under acidic conditions (pH 5.5) compared to neutral conditions (pH 7.0). Microarray analysis not only confirmed previously identified acid-inducible genes but also uncovered many new acid-induced genes which may be directly involved in Agrobacterium-plant interactions. These genes include virE0, virE1, virH1, and virH2. Further, the chvG-chvI two-component system, previously shown to be critical for virulence, was also induced under acid conditions. Interestingly, acidic conditions induced a type VI secretion system and a putative nonheme catalase. We provide evidence suggesting that acid-induced gene expression was independent of the VirA-VirG two-component system. Our results, together with previous data, support the hypothesis that there is three-step sequential activation of the vir regulon. This process involves a cascade regulation and hierarchical signaling pathway featuring initial direct activation of the VirA-VirG system by the acid-activated ChvG-ChvI system. Our data strengthen the notion that Agrobacterium has evolved a mechanism to perceive and subvert the acidic conditions of the rhizosphere to an important signal that initiates and directs the early virulence program, culminating in T-DNA transfer.

Indole-3-acetic acid in plant–pathogen interactions: a key molecule for in planta bacterial virulence and fitness

“…Regarding plant-associated bacteria, IAA has been shown to determine changes in bacterial gene expression in the nongall-forming phytopathogen D. dadantii (formerly Erwinia herbicola) 3937 [57], in Agrobacterium tumefaciens [58,59] and in the plant growth-stimulating rhizobacterium A. brasilense [60], in which its ipdC gene has been the only bacterial gene reported to possess an AuxRE in its promoter, as observed in the auxin-responsive genes of plants [48]. Similarly, in the yeast Saccharomyces cerevisiae, several IAA-inducible genes are regulated at high IAA concentrations by the fungal transcriptional activator YAP-1, which is able to bind to their promoters to induce a switch towards invasive behavior, together with an arrest of cell growth.…”

Indole-3-acetic acid: A widespread physiological code in interactions of fungi with other organisms

“…10,11 In addition, several studies have shown that IAA is a signaling molecule in microorganisms because it affects gene expression in several microorganisms. 12,13 IAA can have a major impact on interactions between IAA-producing organisms. The auxin acts as an effector molecule between IAA-producing bacteria and plants, and bacteria -bacteria interactions have been discussed in several reviews.…”

Morfología y bioactividad de la cianobacteria Leptolyngbya en los campos de cultivo de arroz

“…The production of larger quantities of IAA at lower pH may be attributed to the natural ability of microbes to efficiently express the IAA synthesis in rhizospheric conditions (Yuan, Liu, Saenkham, Kerr, & Nester, 2008). The lightdark regime of 8-16 hours gave the highest synthesis of IAA.…”